A farmer walks through a marijuana field in Mexico.A top U.S. drug official made a strong case Thursday for continued cooperation with Mexico on fighting drug-trafficking, saying successful law enforcement already has created a virtual wall.In a subtle dig at the Trump administration, William Brownfield, the State department's senior diplomat involved in drug policy,&nbsp;said that despite a crisis drug epidemic, the United States and Mexico were in a better position than ever to combat&nbsp;it."In a sense, we have developed a law enforcement cooperative wall at this point without actually having the physical construction of a wall," Brownfield said.Brownfield, assistant secretary of State for international narcotics and law enforcement, spoke to reporters as his agency released the 32nd annual narcotics-control strategy report.Brownfield said the U.S. and Mexico had developed an extended system of intelligence-sharing and joint operations&nbsp;to counter&nbsp;illegal drug trafficking in the last decade&nbsp;since the beginning of the Merida Initiative, an aid program dedicated to law enforcement and the so-called war on drugs.Any future efforts, he said, should be coordinated with Mexican authorities. That contrasts with what President Trump often describes as a unilateral approach to stopping drugs from flowing into the country.Still, Brownfield&nbsp;acknowledged that the U.S.is suffering its worst heroin and opioid&nbsp;crisis in 60 years. Almost all the heroin consumed in the United States &mdash;&nbsp;90% to 94% &mdash;&nbsp;comes from Mexico, he said.Brownfield dodged questions about how possible budget cuts at&nbsp;the State Department would hurt his agency's work. He also had praise for the anti-narcotics trafficking efforts of the United Nations &mdash;&nbsp;another potential target of the administration's budget cutting.